Wastewater treatment plants struggle every day with substances that don’t simply disappear from the water. The removal of nitrogen compounds is very important at these plants. If too much of these substances remains in the water, they harm rivers and the life within them. Karel Havlíček from CXI TUL was a co-investigator on the HYMNA project, which combined two well-known treatment technologies into a single system. And he added something to them that isn’t commonly used at treatment plants: nanofibers.
The full name of the project is “Hybrid MBR-MBBR System Using Nanomaterials for Advanced Wastewater Treatment.” The acronym is HYMNA. “It sounds a bit grand,” laughs co-investigator Karel Havlíček from the Department of Environmental Protection Technology. But the goal was indeed grand. The water that flows out of a treatment plant isn’t always as clean as it could be. And that’s a problem worth solving.
A Screen and Beads
Behind the acronyms MBR and MBBR lie two technologies that treatment plants typically deploy separately. But Karel combined them into a single process and demonstrated that together they can work significantly better. He validated the combination in practice and used it to design a technology with a clear procedure, measurable results, and the potential for real-world application.
The MBR functions as a fine screen. The membranes trap impurities, organic matter, and undissolved particles. But even then, the process isn’t complete—nitrogenous compounds still remain in the clarified water.
To address this, Karel Havlíček and his partners implemented the second part of the technology: MBBR. Small plastic beads with holes and nanofibers inside move freely in the tank with the help of aeration. Microorganisms grow and live on the surface of the nanofibers, converting ammonia nitrogen into nitrates.
Why does this matter? Ammoniacal nitrogen is toxic to fish; it damages their gills and, at higher concentrations, kills them. An excess of nitrogen triggers algae blooms, causing the water to turn green, depleting oxygen levels, and suffocating aquatic life.
Beads with a Nanofiber Core
The beads are no accident. Karel inserted nanofiber carriers—a fine fibrous material to which microorganisms quickly and firmly attach—into plastic bodies with holes. He had already proposed this concept in his dissertation.
The path to the final design was not straightforward. Originally, it was a nanofiber layer. However, it gradually washed off the beads. They replaced it with yarn, which holds its shape. The result is a utility model for new biomass carriers.
The main advantage is the speed of colonization. On conventional materials, colonization takes much longer. Microorganisms colonize the nanofibers quickly. This is crucial, especially where the water is hostile or toxic to them.
Industrial wastewater is often so polluted that bacteria cannot survive on conventional carriers. On a nanofiber surface, however, they manage to attach themselves before the environment destroys them. The system then works even where other technologies would fail.
A Surprising Number
The most important factor was how the system would handle ammonia nitrogen. The team even tested extreme concentrations of up to eighty milligrams per liter. And that’s not just fine-tuning. That’s a stress test pushing the limits—one that could cripple or completely halt the activity of the purifying microorganisms.
The system handled it. At the outflow, they measured less than one milligram per liter.
“We achieved a level that even a conventional treatment plant often can’t handle,” Karel said, expressing his surprise.
Container-Based Treatment Plant
Combining the two technologies brought an added benefit. The system can function not only as a post-treatment unit following a standard treatment plant but also as a standalone modular treatment plant. No construction is needed; the system can be delivered, connected, and put into operation.
“Industrial facilities will especially appreciate this. Companies that currently transport contaminated water in barrels as hazardous waste could handle part of the treatment themselves,” explains Karel. According to him, this would mean less waste, less logistics, and lower costs for companies.
A Myth That Didn’t Pan Out
Apart from the main project, Karel’s team asked themselves another question: Can microorganisms in a standard wastewater treatment plant biofilm on carriers break down micropollutants—that is, traces of medications or pesticides that end up in the water?
Some studies suggested that this might be possible.
But the enthusiasm quickly faded. “No degradation occurs. The micropollutants simply accumulate in the system,” Karel states. The system captures them but does not destroy them. That requires more powerful methods, such as ozone or UV radiation.
The HYMNA project, part of the TREND program of the Technology Agency of the Czech Republic, in collaboration with ENVI-PUR, s.r.o. (principal investigator) and Pražské vodovody a kanalizace, a.s.
